Minimally invasive, image-guided surgery (IGS) offers potential benefits to surgeons and patients alike by providing improved visualization of a surgical target, critical structures surrounding the surgical target, as well as the positioning of instruments used during the surgery, thereby leading to improved surgical accuracy, patient safety, patient recovery, and clinical outcome. Applications of IGS include a wide spectrum of surgical interventions, such as intracranial, head and neck, orthopaedic, spine, and thoracic surgeries. Among the systems enabling next-generation IGS are intraoperative imaging systems, such as mobile C-arms capable of 3D imaging, and guidance systems that register real-time tracking with intraoperative images.
An integral part of IGS is the tracking system. Well known tracking systems include the Polaris Spectra (Northern Digital (NDI), Waterloo, ON Canada), which is based on a stereoscopic infrared camera and retro-reflective markers attached to tracked tools, and the MicronTracker (Claron Technology Inc., Toronto, ON Canada), which is based on a stereoscopic video camera and checkerboard markers. Such systems demonstrate excellent geometric accuracy (about 0.5-2 mm target registration error (TRE)) but suffer potential limitations associated with line of sight obstruction and the inability to track flexible devices within the body. As a result, such optical trackers are typically limited to externalized, rigid tools, such as, for example, rigid pointers and other devices having handles (and markers) that remain outside the body.
The accuracy required in clinical procedures is strongly dependent on the application and surgical site. For example, a previous geometric model has calculated the allowable translational and rotational errors for safe pedicle screw insertion to range from 0.0 mm/0.0° at the T5 vertebra to 3.8 mm/22.7° at the L5 vertebra. The geometric accuracy of tracking systems achieved in practice is typically about 1.5 mm in association with external, rigid tools, such as, for example, rigid pointers or frames. Electromagnetic (EM) trackers provide increased flexibility in tool design due to the use of a small EM sensor and freedom from line-of-sight obstruction. While EM trackers can exhibit somewhat reduced geometric accuracy (about 1-2 mm TRE for the Aurora EM tracking system, NDI) and susceptibility to EM field distortion in the presence of metallic objects, they permit implementations on flexible internal devices (e.g., a bronchoscope) and have shown clinically acceptable accuracy under optimal conditions. Previous studies have examined the influence of specific application settings and the use of specific surgical tools on tracker position and orientation accuracy.
A conventional EM tracker arrangement places an electromagnetic field generator (EMFG) on a mechanical arm over an operating table. The EMFG is draped in proximity to the sterile field. This setup has also been extended to C-arm cone-beam computed tomography (CBCT) by moving the tracker just outside the C-arm field-of-view (FOV). The EMFG typically includes a mass of metallic coils that are not x-ray compatible, necessitating that it be moved during x-ray imaging or positioned out of the x-ray FOV such that the tracker FOV still encompasses the surgical field.
An exemplary setup of a conventional EMFG mounted at tableside is shown in FIG. 1. The setup is shown within the context of x-ray fluoroscopy and/or CBCT. The region of the patient including the surgical target is placed within the FOV (“measurement volume”) of the EM tracker (and the fluoroscopy/CT system). The Aurora EMFG is shown (NDI, Waterloo ON), along with an EM tracker control unit, tracked wired tools, two power cables, and a serial communication cable to personal computer (PC).
This conventional EM tracker arrangement has many limitations. First, arranging essential components of the EM tracking system is time-consuming and makes operating rooms complicated—an EMFG, an EM tracker control unit, wired tracked tools, two power cables, and a serial communication cable to PC must be arranged in an operating site so as to avoid other medical equipment. Second, the complicated setup limits intraoperative use of image-guided surgical system—the cables, tripod, and/or support arm needed to hold the EMFG can be incompatible with X-ray fluoroscopy, computed tomography (CT), and/or CBCT when the EMFG is in place. Thus, the EMFG must generally be positioned outside of the X-ray field. Additionally, the conventional position of the EMFG over the table limits space and access to the patient. Further, mounting of the EMFG above the table on a support arm introduces potential sterility challenges—the system must be bagged and protected from non-sterile exposure.
Accordingly, there is a need in the pertinent art for electromagnetic tracking systems and methods that improve space and access to the patient while preserving the sterility of the surgical field. There is a further need in the pertinent art for electromagnetic tracking systems and methods that are compatible with X-ray imaging techniques, thereby permitting intraoperative usage of such systems and methods.